Method and device for measuring a tubular strand

A device for measuring a strand that is tubular includes a first radiation source to emit terahertz radiation in a first measurement region from an inside onto an inner surface of the strand. A first radiation receiver receives terahertz radiation reflected by the strand in a second measurement region. A first evaluation apparatus determines at least one geometric parameter of the strand in the first measurement region. A second radiation source emits terahertz radiation in the second measurement region from an outside onto an outer surface of the strand. A second radiation receiver receives terahertz radiation reflected by the strand in the second measurement region. A second evaluation apparatus determines at least one geometric parameter of the strand in the second measurement region. A third evaluation apparatus determines a change in the at least one geometric parameter of the strand between the first and second measurement regions.